Cubic III‐nitride coupled quantum wells towards unipolar optically pumped lasers

Abstract

AbstractOptical and structural properties of asymmetric coupled cubic‐GaN/‐AlN quantum wells (QW) are studied. The samples are grown by molecular beam epitaxy on a 50 nm c‐GaN buffer on 3C‐SiC substrate. The active region contains 100 periods of a 2.3 nm AlN barrier, a 1.9–2.1 nm silicon doped GaN QW and a 1.0–1.2 nm undoped GaN QW coupled by a 0.9–1.1 nm AlN tunnelling barrier. Phase purity and partial relaxation of the superlattice is observed in reciprocal space maps measured by high resolution X‐ray diffraction. Optical properties of coupled QWs are investigated using cathodoluminescence spectroscopy. A clear shift in the emission energy associated with the thickness of the QWs can be observed. Furthermore clear TM‐polarized infrared absorption in the 0.55–0.87 eV range is observed at room temperature using Fourier transform infrared spectroscopy. The asymmetric shape of the infrared absorptions reveals the existence of a three level system in the QWs and is explained by contributions of the e1–e3 and e2–e3 intersubband transitions. Measured transition energies are compared to model calculations using a Schrödinger–Poisson solver based on an effective mass model (nextnano3).